1. Field of the Invention
The present invention relates to thickeners. More particularly, the invention relates to methods of making nonionic associative thickeners and compositions thereof.
2. Brief Description of the Related Art
Additives may be used to enhance and/or maintain the viscosity of aqueous systems. For example, additives may be used to increase or maintain the viscosity for compositions used in applications including, but not limited to, latex paint, cleaning agents, cosmetics, aqueous pigment pastes, automotive finishes, industrial coatings, printing inks, lubricating greases, textile coatings, pharmaceutical preparations, agricultural formulations, filler dispersion, adhesives, detergents, wax dispersions, drilling fluids, fire-fighting foams, and/or polishes. Such additives are commonly referred to as “thickeners”. Thickeners may improve and/or affect other properties in certain aqueous systems. For example, thickeners used in latex paints may improve and control the viscosity of the paint, protect colloidal action, and improve pigment suspension, leveling, and flow. Thickeners for aqueous systems include natural thickeners, modified natural thickeners, and synthetic thickeners. Examples of natural thickeners include alginates, casein, gum karaya, locust bean gum, and gum tragacanth. Modified natural thickeners may include derivatized cellulose compounds such as methyl cellulose, hydroxyethyl cellulose, and hydroxypropylmethyl cellulose. Examples of synthetic thickeners include carboxy vinyl ether copolymers, acrylic polymers, maleic anhydride styrene copolymers, and polyurethanes.
Synthetic thickeners are described in U.S. Pat. No. 4,079,028 to Emmons et al.; U.S. Pat. No. 5,252,654 to David et al.; U.S. Pat. No. 5,376,709 to Lau et al.; U.S. Pat. No. 5,627,232 to Glancy et al.; U.S. Pat. No. 5,629,373 to Glancy et al.; U.S. Pat. No. 5,753,731 to Yoshioka et al.; U.S. Pat. No. 5,914,373 to Glancy et al.; and U.S. Published Patent Application Nos. 2007-0161745 to Coutelle and 2004-0147662 to Mattingly; and International Publication No. WO 01/12712 to Zody, all of which are incorporated herein by reference.
Although thickeners for aqueous systems have been used to thicken waterborne compositions, improved thickeners for use in waterborne compositions that include high amounts of pigments and/or intensely colored pigments are needed.